Friable caustic soda and method of producing same



Patented Feb. 13, 1934 FRIABLE CAUSTIC SODA AND METHOD OF PRODUCING SAMEJohn W. Koenders, Midland Mich., assignor to The Dow Chemical Company,Midland, Mich, a corporation of Michigan No Drawing. Application October7, 1931 Serial No. 567,524

6 Claims.

The present invention relates to improvements in the finishing ofcaustic soda for use in the arts and in particular to methods oftreating a v caustic soda finishing melt to modify the physicalcharacteristics thereof exhibited after solidification by cooling, andto'the more friable solid product so obtained.

Caustic soda is produced in large quantities by evaporation of a watersolution thereof, during which, after evaporation of a portion of thewater, salt is separated, if present. The final stage of evaporation iscarried out usually in a large iron pot, the temperature being raised toapproximately 870 F. to drive off the last of the water. It iscustomary, in some practices, in order to prepare a clarified finishedproduct, to treat the concentrated soda with sulphur by throwing a fewhandfuls of sulphur into a pot which may contain around 14 tons ofcaustic soda. In case of inadvertent over-treatment with sulphur, alittle sodium nitrate is added. The batch is allowed to cool somewhatand then discharged from the pot by ladling, pumping, or otherwise intoiron drums or other container in which it solidifies. Such drums usuallycontain in the neighborhood of 700 pounds of product. The ladling orpumping temperature is preferably at, or just above, the freezing point,since solidification is then quicker in the drum and there is lessliability to leakage therefrom. The temperature may be ascertained by apyrometer, or pumping or ladling may be started when the molten causticsoda commences to freeze around the cooler edges of the pot. The coldsolidified product is very hard and difficult to break up into piecesfor use in the arts. It was accordingly noted that a friable grade ofcaustic soda more easily crushed than the usual product would find apreferential place in the market.

Among the objects of the invention is the production of a friablecaustic soda product, cheaply and. easily prepared, and unchangedadversely for uses in the arts, as by discoloration, in the softeningprocess.

To the accomplishment of the foregoing and related ends, the invention,then, consists of the features and method hereinafter fully describedand particularly pointed out in the claims, the following descriptionsetting forth in detail several approved combinations of ingredients andmodes embodying my invention, such disclosed combinations and modesconstituting, however, but several of the various ways in which myinvention may be used.

A long investigation was undertaken directed to the discovery of amethod of producing a soft caustic soda at will. Many attempts were madeto soften a batch by adding oils, greases, waxes and the like to the potwithout success, but it was finally discovered that very smallquantities of certain oils could be put into the individual packagesbefore filling with the molten caustic soda and that the eiiect of suchoils was to induce a coarser, crystalline, friable structure, and toproduce thereby a soft caustic soda. I find that such soft product maybe produced both from batches which have not been treated with sulphuror nitrate and from those which have been treated with sulphur or whichhave been overtreated and subsequently corrected by the addi- 7i! tionof a small quantity of nitrate. Large amounts of nitrate, for example,more than about four handfuls per 14 ton pot, have a negative actionfully or partially preventing or neutralizing the softening action ofthe oil, but it is perfectly feasible to product soft caustic soda fromsuch a batch which has been over-treated with sulphur and corrected withsmall amounts, say up to 4 handfuls, of nitrate.

Although many oils, greases and the like in varying amounts areeffective in varying degrees, I have found that a mineral oil,particularly what is known as heavy motor oil, is so effective that halfa teaspoonful placed in an empty drum will soften 700 lbs. of causticsoda satisfactorily. I

have found further that a parafiin oil, such as the medicinal productknown as American oil, is effective, but to a somewhat less degree thanthe heavy motor oil, and that animal oils and vegetable oils are alsoeffective; for example,

whale oil or castor oil when placed in the drum in small amounts willproduce soft caustic soda.

The following example illustrates the practice of my method and theproduct thereby obtained,

but is not to be taken as limiting, being but one of many runs employingvarious oils successfully.

Electrolytic caustic soda previously concentrated to eliminate salt wasboiled down in an iron kettle until it tested about 77 per cent NazO, NY& L, at which test it had the following approximate analysis:-

96.2 per cent NaOH cent Na2O, actual) Such product constitutes one gradeof substantially anhydrous caustic soda as produced in large quantitiesfor general use in the arts. The 110 batch was treated in the usual wayto clarify it and then allowed to cool to the neighborhood of 600 R,which is the approximate freezing point, whereupon it was pumped intosheet iron drums holding about 700 pounds of caustic soda each, intoeach of which, with the exception of a few, one-half teaspoonful ofheavy motor oil had been previously introduced. After solidifying andfurther cooling, the caustic soda in the drums to which the oil had beenadded was found to be relatively soft and easily broken up with a sledgeinto pieces having a changed, distinctly crystalline fracture, whereasthe caustic soda in those drums without oil was very hard, difficult tobreak up, and showed a rock-like fracture.

Other batches were treated with American oil, whale oil, palm oil,petrolatum, stearic acid, oleic acid, castor oil, cod-liver oil, cupgrease, paraflin, Vaseline, light motor oil, and other substances, butit was found that more American oil or light motor oil was required thanheavy motor oil. In some cases discoloration was more marked than inothers, but the heavy motor oil gave the best result with a minimumamount of oil, using one-half teaspoonful, i. e. about 2.5 cc. per 700pounds. American oil came next in effectiveness but slightly morethereof was required and the product showed some discoloration at thetop of the drum. Whale oil and castor oil gave soft caustic soda which,however, showed with the castor oil a considerable discoloration andwith the whale oil but slight discoloration. The heavy motor oil andAmerican oil gave slight, if any, discoloration.

Further experiments involving the addition of the above named oils tothe batch in the finishing pot did not produce soft caustic soda.Batches that had been inadvertently overtreated with sulphur andcorrected with nitrate, when filled into iron drums containing a smallamount of oil, as above described, gave a soft product if the nitratewas in small amount, but if over 4 handfuls, i. e. about 415 grams, wereused in the pot of 14 to 15 tons capacity, the results were not so good.Batches which had not been treated with sulphur, when filled into drumscontaining a small amount of the oil, also gave a soft caustic sodaproduct.

The invention accordingly provides a method of producing soft causticsoda from batches either with or without previous treatment withsulphur, including those which have been reoxidized with nitrate afterover-treatment with sulphur. The product has a clean appearance uponbreaking up, has a fibrous crystalline structure, is softer than theuntreated material, much more easily broken or crushed and is preferredin the arts for certain uses. The treatment is inexpensive and does notunfit the product for its customary uses.

Xray diffraction pattems have been taken of the ordinary caustic sodaand of soft caustic soda prepared from the ordinary grade in accordancewith my treatment.

These patterns indicate that both products have a crystalline structure,the difference being that the micro crystals of the soft product have apreferred orientation, possessing a fibre axis, while those of theordinary product do not exhibit orientation. The actual size of crystalswas not determined nor the crystal system to which they correspond. Thesoft product fracture exhibits a long, somewhat fibre-like, or laminarstructure, whereas the ordinary product exhibits an amorphous, ormarble-like fracture.

A packaged soft, solid caustic soda may be produced as described bysolidifying in iron drums in the presence of a small amount of an oil.If, however, it be desired, the solidification may take place in any waymore convenient to the subsequent use or treatment. It may, forinstance, be solidified in molds to form cakes, slabs, bars, etc., andthe soft caustic soda thereby produced may be then crushed, broken orground up, if desired. It may also be solidified upon a fiaker toproduce a softer grade of flake caustic soda. The invention isconceived, moreover, to cover not only a method of producing softcaustic soda by solidifying it in the presence of a small amount of anoil, but to cover also upon the product so obtained whether in the formof caustic soda solidified in a package, in a mold, on a fiaker, orotherwise.

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the materials,step, or steps, employed, provided the materials, step, or steps, statedby any of the following claims or the equivalent of such materials,step, or steps, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. Solid caustic soda having a fibrous crystalline structure thecrystals of which exhibit a preferred orientation and possess a definitefibre axis as shown by an X-ray diffraction pattern, such caustic sodabeing characterized by being softer and more easily crushed than theordinary product.

2. The method of producing a relatively soft and friable solid causticsoda which comprises charging molten caustic soda into a container towhich has been added a relatively small amount of an oil and solidifyingthe molten material therein by cooling.

3. The method of producing a relatively soft and friable solid causticsoda which comprises charging molten caustic soda into a container towhich has been added a relatively small amount of a mineral oil andsolidifying the molten material therein by cooling.

4. The method of producing a relatively soft and friable solid causticsoda which comprises charging molten caustic soda into a container towhich has been added a relatively small amount of paraffin oil andsolidifying the molten material therein by cooling.

5. The method of producing a relatively soft and friable solid causticsoda which comprises charging molten caustic soda into a container towhich has been added a relatively small amount of a heavy motor oil andsolidifying the molten material therein by cooling.

6. In a method of filling molten caustic soda into a container, the stepwhich consists in adding a relatively small amount of an oil to thecontainer prior to introducing the molten caustic soda thereinto.

JOHN W. KOENDERS.

